This invention relates in general to gas turbine engines of the type having generally concentric cylindrical casings defining a bypass air passage and turbine discharge passage and to a support structure located downstream of the turbine discharge passage.
One form of gas turbine jet engine is the turbofan, sometimes called the "bypass" engine. Such engines include an annular bypass air passage, or simply bypass duct, between an inner liner and the jet engine casing. The discharge air from a low pressure compressor is typically divided between the bypass duct air and a gas generator including a high pressure compressor, combustor and at least one turbine. Hot turbine discharge gases and the cold bypass air are rejoined or mixed downstream of the turbine by means of an annular device called a mixer. In addition to the foregoing, it is known for jet engines to use a means of thrust augmentation which is typically referred to as an afterburner. Thus, it is known that after the fuel/air mixture has passed through the combustion chamber and turbine, there remains some additional thrust potential with hot turbine discharge gases since not all of the available oxygen has been consumed. Therefore with the addition of more fuel and provision of means for igniting the enriched fuel/gas mixture in the afterburner, additional thrust may be realized.
Higher turbine inlet temperatures of more advanced engines result in higher downstream temperatures at the turbine outlet, which may approach turbine inlet temperatures of some current engines. It is therefore important to provide improved cooling of structural frame members as well as other devices in the hot exhaust path and to provide an environment in the case of afterburner engines to decrease the tendency for the occurrence of flashback. Flashback is the movement of the afterburner flame front in an upstream direction past its designed for location at the flameholder. The flashback tendency may increase as the flameholder inlet temperatures approach and surpass auto-ignition levels so that the high exhaust temperature poses not only a flameholder durability problem but a flashback operational limitation. Finally, in addressing these problems it is important not to create additional pressure losses through blockages or flow disturbances in the diffuser section of the afterburner which would degrade the overall performance of the engine.
Accordingly, one object of the present invention is to accommodate increased engine performance by providing an improved support structure for a gas turbine engine.
Another object of the invention is to provide for improved cooling of the support structure.
Another object of the invention is to provide for improved cooling of engine parts downstream from the support structure.
Another object of the invention is to provide an improved support structure for upgraded afterburner inlet diffuser performance.
Another object of the invention is to provide for improved operability of downstream flameholders in engines which include afterburners.
Another object of the invention is to provide a source of cooling air to downstream components in order to reduce the infrared detectability of such devices.